This invention relates to a finish composition for carbon fibers, and in particular to a method of treating the surface of carbon fibers with an aqueous emulsion of an epoxy resin.
Carbon fiber is conventionally produced by subjecting an organic polymer fiber to various conditions of temperature and atmosphere. Thus, for example, polyacrylonitrile fiber may be heated at a temperature in the range of 200.degree. to 300.degree. C. in an oxidizing atmosphere and subsequently heated at a temperature of at least 1000.degree. C. in an inert atmosphere to give carbon fiber.
It is known to provide carbon fibers with a sizing to facilitate handling and processing. When such fibers are processed without application of a sizing, they tend to fuzz and may actually separate or break as they are pulled over pulleys, rollers, etc.
In many applications, carbon fibers, filaments, yarns to tows are woven into a fabric or tape or otherwise interlaced or overlapped such that the strands are in contact with other similar strands. Because of the high moduli, brittleness and relatively poor abrasion resistance of the strands or the fibers which comprise them, they are difficult to handle during their processing and weaving into fabrics and tapes. These problems have been overcome in the past by the application to the fibers of a size.
U.S. Pat. No. 4,145,472 to R. G. Spain and A. L. Miller describes problems encountered using solutions of sizing materials which contain organic solvents and states that in order to avoid the problems encountered with such solutions, aqueous emulsions have been used as sizings such as aqueous emulsions of epoxy resins. However, problems have been encountered using aqueous emulsions, e.g., the emulsifying agents which are present on the coated fibers after they are dried may seriously degrade the properties of composites ultimately made from the carbon fibers so sized.